JP 2009-5555A discloses an example of a DC-DC converter that performs voltage conversion by driving switching elements. According to the technology disclosed in JP 2009-5555A, in a step-down DC-DC converter that is provided with a plurality of voltage step-down units, a current value is obtained from the high-voltage side and the low-voltage side of a switching element in each voltage step-down unit. Then, whether or not a failure has occurred is monitored by continuously determining whether or not a difference from among the current values is greater than a predetermined value. Upon a failure being detected, the output is limited in order to prevent a non-faulty voltage step-down unit from being overloaded.
In this type of a DC-DC converter, there is the possibility of a current flowing in a reverse direction on the output side. If such a reverse flow occurs, it is preferable that conduction through the reverse flow path can be immediately blocked. However, in the DC-DC converter according to JP 2009-5555A, countermeasures are not taken against such a reverse flow.
The configuration shown in FIG. 3 is an example of the configuration of a DC-DC converter that can block a current when a reverse flow is generated. A DC-DC converter 100 shown in FIG. 3 is an example of a step-down DC-DC converter, and is configured to step down a DC voltage applied to an input line 102A on the primary side, by operating a MOSFET 104 on the high side and a MOSFET 106 on the low side using a synchronous rectification method, and to output the resulting voltage to an output line 102B on the secondary side. The DC-DC converter 100 monitors a current flowing through the secondary-side output line 102B, using a current detection unit (not shown). If a current flows in a reverse direction, the DC-DC converter 100 performs control to block a switching element 110 for protection.
However, in the step-down DC-DC converter 100 shown in FIG. 3, a current flowing through the output line 102B on the secondary side (the low-voltage side) is larger than a current flowing through the input line 102A on the primary side (the high-voltage side). Therefore, if, as in the configuration shown in FIG. 3, the switching element 110 for protection is provided on a path on the secondary side (the low-voltage side) through which a large current flows, conduction loss in the switching element 110 increases, and the amount of heat generated due to the conduction loss also increases.
The present invention has been made in view of the above-described situation, and aims to realize a DC-DC converter that is provided with a reverse flow protection function, while reducing conduction loss.